1. Technical Field
The present invention relates to a technique of driving an electrical load having a capacitive component (capacitive load).
2. Related Art
JP-A-7-130484 discloses a technique in which a plurality of capacitors connected in parallel are previously charged by using a power supply and the capacitors are switched from parallel connection to series connection as needed to generate a voltage higher than a voltage of the power supply, thereby driving an electrical load. By using the proposed technique, it is possible to generate a voltage many times higher than a voltage generated by the power supply according to the number of capacitors connected in series and apply the voltage to the electrical load.
In the proposed technique, however, it is difficult to expand an applicable voltage range as well as to improve the resolution of voltage change. When the voltage to be charged to the capacitor is increased for expanding the applicable voltage range, the resolution of voltage change decreases. Therefore, it is difficult to change the applied voltage in small steps. When the voltage to be charged to the capacitor is decreased for enhancing the resolution of voltage change, the applicable voltage range becomes narrow. It is apparent that when many capacitors are prepared to be connected in series, the applicable voltage range can be expanded while keeping the voltage to be charged to the capacitor low (that is, while keeping the resolution of voltage change high). However, this increases the size of a driving circuit because of a great increase in the number of capacitors.